The Lake Ontario Watershed

Every river and stream on either side of the border whose water ends up in Lake Ontario, over the floor of the lake it ends up in. The gold line is the divide. Rain a step outside it goes to Lake Erie, the Ottawa, the Susquehanna or the Atlantic instead.

—miles of stream

—lakes & ponds

—square miles

Why the streams thicken

a first springthe Trent

Every stream is drawn as wide as the water above it. Neither survey ships a usable stream order, so the network was rebuilt here by snapping — reaches end to end and accumulating length downhill. The Trent reaches Lake Ontario with — miles of stream behind it, the most in the basin.

The floor of the lake

the shore244 m

Lake Ontario is shaded by NOAA's 3 arc-second soundings, with a line every 25 metres. It holds — square kilometres of water and the deepest cell in the grid is 243.9 m, against the 244 the lake is published at.

Biggest by the miles above them

The Ontario Hydro Network names 6% of its reaches against NHD's 24%, so the Canadian rivers are thin in this list and the Trent is missing from it: through the Kawartha lakes it is a chain of unnamed virtual flow lines.

Dim everything outside the divide Show the land underneath The same map of all five lakes Get it at print size, 24 by 20 inches

Divide: USGS Watershed Boundary Dataset, HUC4 0413, 0414, 0427 and 0428. Water: USGS NHD in the United States, Ontario Hydro Network in Canada. Lake floor: NOAA NCEI. Relief © Esri. © Ryan Sajdak 2026 · ☕ Coffee